Tuesday, 10 November 2009

How will you detect or how to debug where the core dump occures?Please follow the steps:-

GDB is the GNU debugger, which is a terminal-based debugger. DDD is a graphical (GUI) front end to GDB.

Normal invocation

The simplest way to run an application under GDB is like so:

$ gdb /usr/local/sbin/snmpd(gdb) run -f -Lo

The '-f' is necessary to prevent snmpd from forking into the background, and '-Lo' tells snmpd to send log messages to STDOUT (i.e. print them in the GDB console window).

Libtool invocation

Net-SNMP uses libtool while building it's applications. This means that sometimes the applications in the source/build directory are not actually binaries, but shell scripts. The libtool script does some magic so that the applications will run using the shared libraries in the build directory, instead of any libraries installed on the system. To run an application with GDB, you have to run GDB through libtool, like so:

$ ./libtool gdb agent/snmpd(gdb) run -f -Lo

Getting a backtrace (aka stack trace)

Once you have got an application running under GDB, you can easily get a backtrace, which will display the sequence of functions that were called to arrive at the point where the debugger is currently stopped.

If an application has crashed, often it will leave a core file. This core file can usually be loaded into GDB to get debugging information after the fact. Simply add the path to the core file after the path to the application when starting GDB.

$ gdb /usr/local/sbin/snmpd /tmp/core.70816

Often this will tell you why the application crashed (e.g. SIGSEGV, aka signal 11). You can then get a backtrace to send to one of the mailing lists for interpretation.

If testing snmpd (or another application) from within the source tree, you'll need to run gdb via libtool:

Introduction

This is a very short introduction into using gdb. Target audience is a unix user which has a serious problem with some application and wants to help fixing the issue by giving detailed informations to the developer or maintainer of the application.

Debug information

Unix binaries can have debug informations attached. gdb can use the debug informations to provide more detailed informations (like function prototypes, source file names and line numbers, ...), thus it is generally a good idea to use a binary which has debug informations.

gcc has a command line switch (-g) which will make gcc write debug informations into object files and executables. It is common practice in the free software community to compile projects with debug info, but strip it off when installing with "make install". Thus you'll usually see a big file size difference between the executables within the source tree and the installed ones, and using the executables from the source tree with gdb gives better results.

Analyzing a segfault

The linux kernel is able to write a so called core dump if some application crashes. This core dump records the state of the process at the time of the crash. gdb can read such a core dump and get informations out of it.

Most distributions have core dumps disabled by default, thus you'll have to reenable them first. "ulimit -c unlimited" will do that for the current shell and all processes started from it. Check the bash manpage if you want to know more about the ulimit command.

The next time some application crashes with a segfault you'll see that the message "Segmentation fault" changed to "Segmentation fault (core dumped)" and you'll find a file named "core" or "core.pid" in the current directory. Note: You need also write access for the current directory, otherwise that isn't going to happen.

Now it is time to start gdb to see what exactly happened. The first argument for gdb should be the executable of the crashed application, the second the core dump written due to the crash. gdb will read alot of informations and will great you with a "(gdb)" prompt when it is done. The most useful piece of information for a developer is a so called stacktrace. Typing "bt" at the prompt asks gdb to print one (which you can mail to the developer). With "quit" you'll leave gdb.

Other ways to use gdb

You can start a application completely under gdb's control. To do that just type "gdb executable". At the gdb prompt type "run arguments" to start the application. If the application receives some signal gdb will give you a prompt asking for commands. You can also type Ctrl-C at any time to get a gdb prompt. The most useful gdb commands are:

bt

print a stacktrace (as mentioned above).

c

continue running the application.

print expression

print the value of the specified expression. Can be used to inspect the value of certain variables for example, simply specify the variable name as expression

quit

quit gdb.

It is also possibel to attach gdb to a already running process. This can be done with "gdb executable pid". gdb will attach to the process specified by the process id. That might be useful it some application seems to be stuck in a endless loop and you want to figure where exactly it hangs.

Advanced gdb debugging

If you start to do more things with gdb than just printing a stacktrace you likely notice some odd effects like not being able to inspect certain variables. That may happen due to compiler optimizations. If gcc decides to make a variable a register variable (i.e. never store it somewhere in memory) gdb will not see it. To avoid that rebuild the application you are going to debug without optimizations.

More common gdb commands are:

s

single step though the application.

break argument

set breakpoints, i.e. make the application stop (and gdb give you a prompt) once it reaches some specific point, some function for example.

watch expression

set a watchpoint, i.e. stop if expression has changed. Can be used to catch the line of code which modifies some variable for example.

up, down

walk up and down in the stack, to inspect variables in other places of the stack too, not just the current function.

help

gdb online help. Go read there all the details, the scope of this document ends just here :-)BTW: a nice info manual for gdb is available too.

print a log of all (or selected) system calls some application performes.One common programming mistake is missing error handling, not checking the return value of system calls for example. Instead of notifying the user with a message like "opening file foo failed with error bar" applications simply assume that opening the file worked and just crash later if it didn't. That kind of bug often can easily be found with strace because you'll see the system call return values in the strace log.Of course strace is useful for alot of other purposes too.

Tuesday, 27 October 2009

mkdir:-----------------------amaresh@eOdissa:~/Documents/Test$ mkdir --helpUsage: mkdir [OPTION] DIRECTORY...Create the DIRECTORY(ies), if they do not already exist.

Mandatory arguments to long options are mandatory for short options too. -m, --mode=MODE set file mode (as in chmod), not a=rwx - umask -p, --parents no error if existing, make parent directories as needed -v, --verbose print a message for each created directory -Z, --context=CTX set the SELinux security context of each created directory to CTX --help display this help and exit --version output version information and exit

cd - Change working directory:----------------------------------------------------------cd - Change working directory, cd :- will got respective dir cd .. :- will go to one position dirctory to current dirctory cd - :- will go to Old pwd from new pwd

If you are using Linux and you need to resize a hundred images or so, you can certainly use Gimp, but that would be too much work. Consider ImageMagick set of graphic tools. You can install ImageMagick on Ubuntu by going to the Terminal and typing: “sudo apt-get install imagemagick.” Once the application is installed, all you need to do is go to your image directory and execute the following command:

mogrify -resize 900×600 *.jpg

This command will resize any image with a .jpg extension to a size of 900×600 pixels.

How will you get only UDP protocol status in a network ?Ans:- # netstat -uO/P:-root@eOdissa-desktop:/home/amaresh/Documents/Testing# netstat -uActive Internet connections (w/o servers)Proto Recv-Q Send-Q Local Address Foreign Address State

Monday, 3 August 2009

Hi,We have 8 positions for .Net in our team (2 – 6 yrs experience).Kindly refer your friends who have worked on .net desktop applications.WPF, WCF, Silverlight, XBAP will be added advantage.Also we have 5 openings for linux, c, c++ with network programming skills ( 2- 6 yrs). Kindly refer for this as well.Please forward this to your friends.CV’s can be sent to kmjeetendra@tycoint.comThanks & RegardsJeet

Thursday, 30 July 2009

Greetings!!We are having openings for one of our company,PuneCompany:Keypair TechnologiesLocation:PunePosition:Tech Lead/DeveloperEXp: 2-10 yrsURL:www.keypairtech.com, www.fortifyis.com

About the Company:

Located in Santa Clara, CA, Key Pair Technologies is a VC funded startup in stealth mode to address business needs in the area of multi-form factor and protocol authentication. We are looking for highly motivated and talented Software Developers who are excited to work on networking and authentication technologies to solve business problems.

The ideal candidate has strong C/C++ development skills and has experience developing commercial Linux/Unix based products or appliances. You will join a team developing the leading edge distributed and high performance Linux based platform to enable strong multi-form factor and protocol authentication.

Applicant will have a strong application design and development background (preferably on Linux) and will have the ability to provide technical leadership in solving engineering problems. Just as important are non-technical life skills such as the ability to lead a project, meet deadlines, work with a team, and communicate clearly both verbally and on paper.

* 3+ years of software development experience in Networking and Network security field. * Demonstrated excellence in C and C++ design, patterns, coding, debugging and unit testing. * Skills with scripting language such as GnuMake, Perl or Python* Skills in L4-L7 packet processing, UDP/TCP sockets, multi-threading, process control, IPC, signals, system calls and multiprocessing in Linux environment using C/C++. * Knowledge of application layer protocols such as HTTP, TLS, WS-* and technologies such as Open SSL is desired * Knowledge of Authentication methodologies such as RADIUS, SAML, Kerberos is desired. * Experience with large scale systems, scalability, availability and performance issues with Linux is desired. * Ability to complete software projects on time in a fast paced environment.

Desirable Skills:

* Knowledge of Java/J2EE is desired. * Ability to complete software projects on time in a fast paced environment

If you are interested please forward me your updated CV ASAP.If not please ignore this mail.

Prithvi is a US$ 279 million, global provider of IT Consulting and Engineering solutions company. Prithvi's decade of experience helps it to continually innovate and address latest imperatives in IT industry.Our operations began in the year 1998 with our registered office in Hyderabad, India and US head office located in Pittsburgh (PA). Prithvi's global network of development centers and sales offices are in Europe, Middle East and Asia Pacific.Prithvi Professional Services provides strategic and innovative staffing solutions. We offer a complete staffing solution to meet your ever-changing technology demand and highest level of customer satisfaction.We specialize in worldwide IT solutions and engineering services staffing. We follow a stringent hiring, grooming and deployment process which includes technical tests and multiple rounds of interviews, to ensure an excellent match.www.prithvisolutions.com

Tuesday, 21 July 2009

This command allows you to change your login password. You are prompted to enter your current password, and then prompted (twice) to enter your new password. On Linux systems (like haribol) passwords should exceed 6 characters in length, and contain at least one non-alphanumeric character (such as #, %, *, ^, [, or @ etc.)

cd

This command, as in DOS, changes directories. You can use .. to represent the directory above the current directory. You can use ~ to represent your root directory (also called your home or top directory). Example: cd maindir to move into the maindir directory, cd .. to move to the directory above, or cd ~ to move to your root directory.

pwd

This command tells you which directory you are currently working in. Your home directory is represented by the tilde ~ symbol. To go to your home directory from anywhere, type cd ~, however typing cd without the ~ also works on Linux systems.

ls

This gives you a listing of all files in a directory. You can't tell which are files and which are directories.

ls -F

This shows which files are normal files (they have no special symbols at the end), which are directories (they end in a / character), which are links (they end in a @ symbol) and which are executables (they end in a * character). These special symbols are NOT part of the file name.

ls -l

"Long" format. Gives more details about files and directories in the current directory.

ls -a

Lists "hidden" files in current directory (those starting with a . character).

ls -la

Options may usually be combined. This particular combination would list both hidden and unhidden files in the long format

mv

The "move" command is how you rename files. Example: mv oldfile.txt newfile.txt

Sends the contents of a file to stdout (usually the display screen). The name comes from "concatenate." Example: cat index.html

more

Like cat but displays a file one page at a time. Example: more long_file.txt

wc

Counts the number of lines, words, and characters in a file. Example: wc essay.rtf

tail -n

Displays the last n lines of a file. Example: tail -5 myfile

head -n

Displays the first n lines of a file. Example: head -5 myfile

mkdir

Creates a new directory, located below the present directory. (Use pwd first to check where you are!) Example: mkdir new_dir

rmdir

Deletes a directory. Example: rmdir old_dir

man

The most importantUnix command! It displays the manual pages for a chosen Unix command. Press [Enter] to advance one line, [Spacebar] to advance one page, and the [Q] key to quit and return to the Unix prompt. Example: man ls

man -k

Displays all Unix commands related to a given keyword. Example: man -k date will list all Unix commands whose man pages contain a reference to the word date.

date

Shows the current time and date.

logout

Terminates the current login session, (and returns you to your telnet client, if that is how you established the session originally).

I/O Redirection

<

Input redirection. This allows you to take input from a file rather than stdin. Example: tr a z

>

Output redirection. This allows you to send output to a file rather than stdout. Example: ls -l >listing

|

Pipe. This allows you to connect stdout from one command with stdin of another. Example: ls -la | more

File Compression:-

gzip filename --- compresses files, so that they take up much less space. Usually text files compress to about half their original size, but it depends very much on the size of the file and the nature of the contents. There are other tools for this purpose, too (e.g. compress), but gzip usually gives the highest compression rate. Gzip produces files with the ending '.gz' appended to the original filename.

gunzip filename --- uncompresses files compressed by gzip.

gzcat filename --- lets you look at a gzipped file without actually having to gunzip it (same as gunzip -c). You can even print it directly, using gzcat filename | lpr

lpr filename --- print. Use the -P option to specify the printer name if you want to use a printer other than your default printer. For example, if you want to print double-sided, use 'lpr -Pvalkyr-d', or if you're at CSLI, you may want to use 'lpr -Pcord115-d'. See 'help printers' for more information about printers and their locations.

lpq --- check out the printer queue, e.g. to get the number needed for removal, or to see how many other files will be printed before yours will come out

lprm jobnumber --- remove something from the printer queue. You can find the job number by using lpq. Theoretically you also have to specify a printer name, but this isn't necessary as long as you use your default printer in the department.

genscript --- converts plain text files into postscript for printing, and gives you some options for formatting. Consider making an alias like alias ecop 'genscript -2 -r \!* | lpr -h -Pvalkyr' to print two pages on one piece of paper.

dvips filename --- print .dvi files (i.e. files produced by LaTeX). You can use dviselect to print only selected pages.

Finding things

ff --- find files anywhere on the system. This can be extremely useful if you've forgotten in which directory you put a file, but do remember the name. In fact, if you use ff -p you don't even need the full name, just the beginning. This can also be useful for finding other things on the system, e.g. documentation.

grep string filename(s) --- looks for the string in the files. This can be useful a lot of purposes, e.g. finding the right file among many, figuring out which is the right version of something, and even doing serious corpus work. grep comes in several varieties (grep, egrep, and fgrep) and has a lot of very flexible options. Check out the man pages if this sounds good to you.

About other people

w --- tells you who's logged in, and what they're doing. Especially useful: the 'idle' part. This allows you to see whether they're actually sitting there typing away at their keyboards right at the moment.

who --- tells you who's logged on, and where they're coming from. Useful if you're looking for someone who's actually physically in the same building as you, or in some other particular location.

finger username --- gives you lots of information about that user, e.g. when they last read their mail and whether they're logged in. Often people put other practical information, such as phone numbers and addresses, in a file called .plan. This information is also displayed by 'finger'.

last -1 username --- tells you when the user last logged on and off and from where. Without any options, last will give you a list of everyone's logins.

talk username --- lets you have a (typed) conversation with another user

elm --- lets you send e-mail messages to people around the world (and, of course, read them). It's not the only mailer you can use, but the one we recommend.

About your (electronic) self

whoami --- returns your username. Sounds useless, but isn't. You may need to find out who it is who forgot to log out somewhere, and make sure *you* have logged out.

finger & .plan filesof course you can finger yourself, too. That can be useful e.g. as a quick check whether you got new mail. Try to create a useful .plan file soon. Look at other people's .plan files for ideas. The file needs to be readable for everyone in order to be visible through 'finger'. Do 'chmod a+r .plan' if necessary. You should realize that this information is accessible from anywhere in the world, not just to other people on turing.

passwd --- lets you change your password, which you should do regularly (at least once a year).

ps -u yourusername --- lists your processes. Contains lots of information about them, including the process ID, which you need if you have to kill a process. Normally, when you have been kicked out of a dialin session or have otherwise managed to get yourself disconnected abruptly, this list will contain the processes you need to kill. Those may include the shell (tcsh or whatever you're using), and anything you were running, for example emacs or elm. Be careful not to kill your current shell - the one with the number closer to the one of the ps command you're currently running. But if it happens, don't panic. Just try again :) If you're using an X-display you may have to kill some X processes before you can start them again. These will show only when you use ps -efl, because they're root processes.

kill PID --- kills (ends) the processes with the ID you gave. This works only for your own processes, of course. Get the ID by using ps. If the process doesn't 'die' properly, use the option -9. But attempt without that option first, because it doesn't give the process a chance to finish possibly important business before dying. You may need to kill processes for example if your modem connection was interrupted and you didn't get logged out properly, which sometimes happens.

quota -v --- show what your disk quota is (i.e. how much space you have to store files), how much you're actually using, and in case you've exceeded your quota (which you'll be given an automatic warning about by the system) how much time you have left to sort them out (by deleting or gzipping some, or moving them to your own computer).

du filename --- shows the disk usage of the files and directories in filename (without argument the current directory is used). du -s gives only a total.

last yourusername --- lists your last logins. Can be a useful memory aid for when you were where, how long you've been working for, and keeping track of your phonebill if you're making a non-local phonecall for dialling in.

Connecting to the outside world

nn --- allows you to read news. It will first let you read the news local to turing, and then the remote news. If you want to read only the local or remote news, you can use nnl or nnr, respectively. To learn more about nn type nn, then \tty{:man}, then \tty{=.*}, then \tty{Z}, then hit the space bar to step through the manual. Or look at the man page.

rlogin hostname --- lets you connect to a remote host

telnet hostname --- also lets you connect to a remote host. Use rlogin whenever possible.

ftp hostname --- lets you download files from a remote host which is set up as an ftp-server. This is a common method for exchanging academic papers and drafts. If you need to make a paper of yours available in this way, you can (temporarily) put a copy in /user/ftp/pub/TMP. For more permanent solutions, ask Emma. The most important commands within ftp are get for getting files from the remote machine, and put for putting them there (mget and mput let you specify more than one file at once). Sounds straightforward, but be sure not to confuse the two, especially when your physical location doesn't correspond to the direction of the ftp connection you're making. ftp just overwrites files with the same filename. If you're transferring anything other than ASCII text, use binary mode.

lynx --- lets you browse the web from an ordinary terminal. Of course you can see only the text, not the pictures. You can type any URL as an argument to the G command. When you're doing this from any Stanford host you can leave out the .stanford.edu part of the URL when connecting to Stanford URLs. Type H at any time to learn more about lynx, and Q to exit.

`history' prints a line for each selected history record. Each linebegins with a character indicating the record type (*note historyoptions::), followed by a timestamp (in the format `YYYY-MM-DD HH:MMZZZZ'), then the name of the user who performed the action. Theremainder of the line depends on the record type:

`T' The relative path to the directory in the repository; then the description of the tag in the format `[NAME:OPT]' where NAME is the tag name and OPT is `D' for `tag -d', the specified revision for `tag -r', the specified date for `tag -D', or `A' for a plain `tag'.

`F', `E', `O' The tag/revision/date checked out, if any, enclosed in `[' and `]'; the relative path to the directory in the repository, if any; the associated module name, enclosed in `=' and `='; then the absolute path to the local working directory or `'.

`W', `U', `P', `C', `G', `M', `A', `R' The revision checked out; the file name; the relative path to the directory in the repository, if any; the associated module name, enclosed in `=' and `='; then the absolute path to the local working directory or `'.

`~' at the beginning of a working directory means the user's homedirectory. `*' at the end of a repository or working directory meansthe associated module name.

Anyway, here it is, for you to downloadthe source.list. You might want to open it in a text editor, so it doesn’t open Synaptic for you. This list uses the Norwegian mirrors. Just add from “3rd party repos” and down.

then do "gedit /etc/apt/source.list"

replace the content of source.list with downloaded file

reboot the system

goto System --> Administration --> Software source ; then click all check post and change the repository to "main server"

After refreshing the package manager's cache, packages from the backport repositories will now be available for installation.

Go to System > Administration > Software Sources

Then, make sure the main, universe, restricted, and multiverse sources are all checked (or ticked). In most cases, you will not need the source code or CD-ROM/DVD sources.

I believe in Ubuntu 9.04 these should be all checked by default.

You should also choose to download from your country's server in the Download from section. This puts a little less strain on the main Canonical servers.

Next, click on the Third-Party Software tab and click Add

In the APT line paste in

deb http://packages.medibuntu.org/ jaunty free non-free

if you're using Ubuntu 9.04.

For Ubuntu 8.10, you should substitute intrepid for jauntyFor Ubuntu 8.04, you should substitute hardy for jaunty

Then click Add Source

Click the Closebutton (next to Revert at the lower-right-hand corner). You'll be prompted to Reload. Go ahead and do so.

Some information will then be downloaded letting your Ubuntu installation know what new software is available for installation.

You will get an error message saying that the public key isn't available for the Medibuntu repositories. That's okay. We're about to fix that.

Go to System > Administration > Synaptic Package Manager

When Synaptic Package Manager opens, click on Search at the top-right corner and when the Find dialogue box appears, search for the word medibuntu and then click Search.

When you find the medibuntu-keyring package in the results, right-click it and select Mark for Installation. Then click Mark again to confirm.

Then click Apply and Apply again to confirm.

Once the keyring is installed,

More about repositories

So what are all of these different repositories anyway? Ubuntu Linux has a commitment to open source software, and so for mainly philosophical (and secondarily sometimes legal) reasons, it doesn't include a lot of proprietary software by default. The Ubuntu development team also can offer full support for only the official Ubuntu repositories (Main and Restricted).

You can read on the Ubuntu website more in-depth descriptions of the different types of repositories. Here's a quick low-down, though:

Main:Freely licensed software that's officially supported.

Restricted:Not exactly freely licensed software that is pretty essential to getting a lot of popular configurations working.

Universe: A lot of freely licensed software that's packaged by the community and not officially supported.

Multiverse: Not freely licensed software, also put together by the Ubuntu community and not officially supported.

Medibuntu:Software not included in the other repositories for various reasons.

There is also a volunteer group that puts together a lot of .deb packages for software not in the repositories or of newer versions than are currently in the repositories. Their software can be found at GetDeb.